The class java.util.Arrays has a asList method that should be use when you want to create a new List from an array of objects. It is faster than executing a loop to cpy all the elements of the array one by one

Use String.indexOf(char) when checking for the index of a single character; it executes faster.

Use StringBuffer.length() to determine StringBuffer length rather than using StringBuffer.toString().equals() or StringBuffer.toString().length() ==.

The imports part of a file should be handled by the Integrated Development Environment (IDE), not manually by the developer. Unused and useless imports should not occur if that is the case. Leaving them in reduces the code's readability, since their presence can be confusing.

The following code snippet illustrates this rule:

package my.company;

import java.lang.String;        // Non-Compliant - java.lang classes are always implicitly imported
import my.company.SomeClass;    // Non-Compliant - same package files are always implicitly imported
import java.io.File;            // Non-Compliant - File is not used

import my.company2.SomeType;
import my.company2.SomeType;    // Non-Compliant - 'SomeType' is already imported

class ExampleClass {

  public String someString;
  public SomeType something;

}

An operation on an Immutable object (BigDecimal or BigInteger) won't change the object itself. The result of the operation is a new object. Therefore, ignoring the operation result is an error.

Useless parentheses can sometimes be misleading and so should be removed.

The following code snippet illustrates this rule:

return 3;             // Compliant
return (x);           // Non-Compliant
return (x + 1);       // Non-Compliant
int x = (y / 2 + 1);  // Non-Compliant
int y = (4+X) * y;    // Compliant

Utility classes, which are a collection of static members, are not meant to be instantiated. They should therefore not have public constructors.

Java adds an implicit public constructor to every class which does not define at least one explicitly. Hence, at least one non-public constructor should be defined.

The following code:

class StringUtils { // Non-Compliant

  public static String concatenate(String s1, String s2) {
    return s1 + s2;
  }

}

should be refactored into:

class StringUtils { // Compliant

  private StringUtils {
  }

  public static String concatenate(String s1, String s2) {
    return s1 + s2;
  }

}